Natural products that have been isolated from the marine environment show promise as pharmacological agents. However, because of the supply problems associated with their isolation, a thorough evaluation of their properties requires their chemical synthesis. This proposal describes the chemical synthesis of three biologically important marine natural products. The first of these is gambierol, a marine ladder toxin associated with ciguatera poisoning. The second is armatol A, a polycyclic ether that has demonstrated interesting cytotoxicity in preliminary testing. The third is halichondrin B, a potent anticancer agent that has been recommended for preclinical trials in spite of its short supply. Gambierol, armatol A, and halichondrin B have in common a fused polycyclic ether skeleton. This proposal outlines the chemical synthesis of these agents centered around carbon-glycosides. As carbon-glycosides have been demonstrated to be important, not only in synthetic chemistry, but also in medicinal chemistry, we believe that this strategy might have broad implications. In addition, by coupling our carbon-glycoside forming chemistry with efficient annulation protocols, we believe that we will be able to efficiently generate polycyclic ethers including the natural products listed above. Furthermore, these efforts will undoubtedly lead to the generation of a number of interesting and biologically important analogs whose properties will be evaluated.